The present invention relates generally to the field of disc drive data storage devices, and more particularly, but not by way of limitation, to an automated assembly of a disc drive head-disc assembly which includes an automated dynamic balance correction station.
Modem hard disc drives are commonly used in a multitude of computer environments ranging from super computers through notebook computers to store large amounts of data in a form that can be made readily available to a user. Typically, a disc drive comprises one or more magnetic discs that are rotated by a spindle motor at a constant high speed. The surface of each disc serves as a data recording surface and is divided into a series of generally concentric recording tracks radially spaced across a band between an inner diameter and an outer diameter. The data tracks extend around the disc and data is stored within the tracks on the disc surface in the form of magnetic flux transitions. The flux transitions are induced by an array of transducers otherwise commonly called read/write heads. Typically, each data track is divided into a number of data sectors that store fixed sized data blocks.
Each read/write head includes an interactive element such as a magnetic transducer which senses the magnetic transitions on a selected data track to read the data stored on the track. Alternatively, the read/write head transmits an electrical signal that induces magnetic transitions on the selected data track to write data to the track. As is known in the art, the read/write heads are supported by rotary actuator arms and are positioned by the actuator arms over a selected data track to either read or write data. The read/write head includes a slider assembly having an air-bearing surface that causes the read/write head to fly relative to the disc surface. The air bearing is developed by load forces applied to the read/write head by a load arm interacting with air currents produced by disc rotation.
Typically, several open-centered discs and spacer rings are alternately stacked on the hub of a spindle motor, followed by the attachment of a clampring to form a disc pack. The hub, defining the core of the stack, serves to align the discs and spacer rings around a common centerline. Movement of the discs and spacer rings is typically constrained by a compressive load maintained by the clampring. The complementary actuator arms of an actuator assembly, commonly called an E-block, support the read/write heads to access the surfaces of the stacked discs of the disc pack. The read/write heads communicate electronically with a printed circuit board assembly (PCB) through read/write wires and a flex circuit attached to the E-block. When the E-block is merged with the disc pack into a base deck and a cover is attached to the base deck, a head-disc assembly (HDA) is formed. For a general discussion of E-block assembly techniques, see U.S. Pat. No. 5,404,636 issued to Stefansky et al. and assigned to the assignee of the present invention.
The head-disc assembly (HDA) of a disc drive is typically assembled in a clean room environment. A clean room environment (free of contaminants of 0.3 micron and larger) is necessary to ensure that the head-disc interface remains unencumbered and damage free. The slightest damage to the surface of a disc or read/write head can result in a catastrophic failure of the disc drive. The primary causes of catastrophic failure, particularly read/write head crashes (a non-recoverable, catastrophic failure of the disc drive) are generally characterized as contamination, exposure to mechanically induced shock and non-shock induced damage. The source of non-shock induced damage is typically traced to the assembly process, and generally stems from handling damage sustained by the disc drive during the assembly process.
Several factors that bear particularly on the problem of assembly process induced damage are the physical size of the disc drive, the spacing of the components, the recording densities sought to be achieved and the level of precision to be maintained during the assembly process. The high levels of precision required by the assembly process are necessary to attain the operational tolerances required by the disc drive. The rigorous operational tolerances are in response to market demands that have driven the need to decrease the physical size of disc drives while simultaneously increasing disc drive storage capacity and performance characteristics.
Demands on disc drive mechanical components and assembly procedures have become increasingly more critical in order to meet the strenuous requirements of increased capability and size reduction in the face of these new market demands. Part-to-part variations in critical functional attributes in the magnitude of micro-inches can result in disc drive failures. Additionally, as disc drive designs continue to require size reduction, smaller read/write heads, thinner substraights, longer and thinner actuator arms, and thinner gimbal assemblies must continue to be incorporated into the drives. This trend significantly exacerbates the need to improve assembly processes to protect the read/write heads and discs from damage resulting from incidental contact between mating components. The aforementioned factors resultantly increase the difficulty of assembling disc drives, and as the assembly process becomes more difficult, the need to invent new tools, methods and control systems to deal with the emerging complexities pose unique problems in need of solutions.
Coupled with the size and performance demands is the further market driven requirement for, ever increasing fault free performance. The progression of continually thinner disc thickness and tighter disc spacing, together with increasing track density and increasing numbers of discs in the disc pack, has resulted in a demand for tools, methods and control systems of ever increasing sophistication. A result has been a decreasing number of assembly tasks involving direct operator intervention. Many of the tasks involved in modern methods are beyond the capability of operators to reliably and repeatedly perform, further driving the need for automated equipment and tooling.
In addition to the difficulties faced in assembling modem disc drives of high capacity and complex, physical product performance requirements have dictated the need to develop new process technologies to ensure compliance with operating specifications. The primary factors driving more stringent demands on the mechanical components and the assembly process are the continually increasing areal densities and data transfer rates of the disc drives.
The continuing trend in the disc drive industry is to develop products with ever increasing areal densities, decreasing access times and increasing rotational speeds. The combination of these factors places greater demands on the ability of modem servo systems to control the position of read/write heads relative to data tracks. The ability to assemble HDAs nominally free from the effects caused by unequal load forces on the read/write heads, disc pack imbalance or one of the components of runout, velocity and acceleration (commonly referred to as RVA) poses a significant challenge as track densities increase. The components of RVA are disc runout (a measure of the motion of the disc along the longitudinal axis of the motor as it rotates); velocity (a measure of variations in linear speed of the disc pack across the surface of the disc); and acceleration (a measure of the relative flatness of the discs in the disc pack). By design, a disc drive typically has a discreet threshold level of resistance to withstand rotationally induced noise and instability, below which the servo system is not impaired. Also, a fixed range of load forces must be maintained on the read/write head to ensure proper fly height for data exchange. The operating performance of the disc drive servo system is affected by mechanical factors beyond the effects of mechanically induced read/write head oscillation from disc surface anomalies. Errors are traceable to disc pack imbalance and RVA noise sources. Even with improved approaches to the generation of position error signals in the disc drive servo system, the ability of the system to deal with such issues is finite. The limits of the servo system capability to reliably control the position of the read/write head relative to the data track must not be consumed by the noise present in the HDA resulting from the assembly process. Consumption of the available margin by the assembly process leaves no margin in the system to accommodate changes in the disc drive attributes over the life of the product. An inability to accommodate changes in the disc drive attributes leads to field failures and an overall loss in product reliability, a detrimental impact to product market position.
Thus, in general, there is a need for an improved approach to disc drive-assembling technology to minimize the potential of damage during assembly, to produce product that is design compliant and reliable, and to minimize mechanically induced system noise. One such need is that of an automated dynamic balance correction of a disc drive.
An automated dynamic balance correction station used to produce balance corrected disc drive assemblies by placing a balance correction member on disc packs displaying an out of balance condition. The balance correction station has a conveyor, a lift and balance measure assembly, a lift and locate assembly, a feature detection assembly and a balance correct assembly. The disc drive assembly includes a disc pack that has a spindle motor with an attached spindle motor hub that has a timing mark and supports a stack of interleaved member parts. The stacked member parts include discs, spacer rings and enlarged stack rings constrained by a clampring that has an annular balance correction containment cavity.
The disc drive is moved via the conveyor to the lift and balance measure assembly where the disc pack is lifted and activated to operational speed. At operational speed the lift and balance measure assembly checks for and measures, if present, the amount of imbalance present in the disc pack. If imbalance is present, the dynamic balance correction station determines the angular position of the source of the imbalance relative to the timing mark. Using the feature detection assembly to determine the angular placement position for the balance correction member relative to the timing mark and using the balance correct assembly to physically place the balance correction member on the disc pack, the dynamic balance correction station dispenses the balance correction member into the annular balance correction containment cavity to form a balance corrected disc pack.
The balance correction member comprises a C-shaped ring formed from a wire of nominally uniform cross-sectional area and has a substantially elliptical shape in an uncompressed state. The balance correct assembly compresses the balance correction member to a substantially circular shape and then places the compressed balance correction member adjacent the disc pack so that the compressed balance correction member expands and compressingly engages an annular recess in the disc pack.